1. Field of the Invention
The invention relates to flanges for attaching an exhaust manifold to an engine block.
2. Discussion of the Prior Art
Exhaust manifolds, which collect the hot exhaust gases emerging from the cylinder outlets of the engine block and conduct these gases to an exhaust system consisting of exhaust pipes, a catalytic converter and a muffler, were originally manufactured as castings. For example, see U.S. Pat. No. 2,847,819. The greatest problem has thereby been presented by the flange, with the help of which the exhaust manifold is screwed to the engine block. Firstly, it must be possible to attach the flange in a gas-tight manner. Secondly, modem engine design calls for flanges of certain thicknesses and shapes, which leads to considerable expense in casting.
For this reason, pipe elbows are being increasingly used. These consist of elbow pipes of suitable length and shape, which are welded to a flange.
Particular demands are also placed on the flange, with the help of which the exhaust manifold is screwed to the engine block. For example, the flanges must be gas-tight and have high intrinsic rigidity. Problems also result from the high temperatures and the associated thermal expansion differences. In this regard, see German reference DE OS 15 76 357, which calls for each cylinder outlet to have its own small flange.
German reference DE 31 29 351 C2 discloses a flange that is divided in the thickness direction. The incoming tubular conduit of the manifold is welded only to one part of the flange. This flange part, in turn, is then welded to the other flange part. In this way, forces created by heat stress are to be better intercepted. Again, each cylinder outlet has its own small-area flange.
Finally, European reference EP 0 178 430 B1 discloses an exhaust manifold with a flange composed of four relatively thin sheet metal plates, which can consist at least partly of high-quality steel. The sheet metal plates are individually stamped, accurately stacked with the help of adjustment borings and adjustment pins and, finally, hard-soldered. The top sheet metal plate is equipped with an eyelet, into which an elbow pipe can be welded. This flange is intended for two cylinder outlets.
In the meantime, of course, it has also proved possible to produce flanges that are composed of sheet metal plates and cover all of the cylinder outlets, e.g., four, in a four-cylinder engine, in a single piece. Exhaust manifolds with such one-piece flanges, however, must be embodied very rigidly, so that the heat expansion resulting from the temperature differences among different individual parts can be absorbed without the flange becoming permeable. Rigidity thereby means heaviness.
Another solution of this problem is described in German reference DE 296 15 840 U. This flange comprises a single deep-drawn metal sheet.